1. Field of the Invention
The present invention relates to digital recording channel electronics, and particularly to parallel to serial conversion for such applications. In digital recording channels of the form utilized with magnetic storage media, such as disk and tape, it is common to encode data internal to the system into particular symbol form to accommodate characteristics of the channels of the system. This is also true with communications systems. For example, with GCR encoding, a number of parallel internal bits such as a byte (8 bits) are usually encoded into a larger number of parallel bits, required to meet constraints imposed by the channel characteristics when tape is the recording media or multiple recording channels are usually employed. In handling the encoded symbols, it is necessary to accomplish parallel to serial conversion, in the sense that a parallel encoded format must be converted to a serial bit stream for shifting onto a given recording channel. When a stream of encoded symbols is provided for multiple channels, the loading of a sequence of the channels is distributed through the period of one of the symbols shifting onto a given channel.
2. Description of the Prior Art
It has been usual, in recording channel design, to utilize a single encoder for producing the desired groups or symbols of encoded bits. This is usually accomplished by using a number of parallel to serial shift registers equal in number to the number of channels. While parallel to serial conversion using such hardware is suitable, it results in fairly high cost for channel hardware inasmuch as a matrix of shift registers for a nine-channel data recording system would include a relatively large number of register cells or flip flops.
Other conversion or multiplexing systems have been utilized. For example, U.S. Pat. No. 3,914,553 describes a network with serial to parallel conversion or parallel to serial. However, in FIG. 2 of that patent a matrix of shift register cells is illustrated which is relatively costly, as well. In addition, U.S. Pat. No. 3,267,460 shows a serial to parallel or parallel to serial digital converter which utilizes a large number of cells in the conversion hardware.
Accordingly, a need exists for a parallel to serial converter for recording channel or time division multiplexed applications with reduced hardware cost.